This invention relates generally to fuel cells and, more specifically, to fuel-oxygen fuel cells.
Fuel cells are taking on increased importance for the production of electrical energy. The simple design of a fuel cell allows for electrical production from a wide variety of sizes and capacities. Moreover, many fuel cells, such as hydrogen-oxygen fuel cells, produce electrical power with virtually no anti-environmental side effects.
The major problem in the use of fuel cells has been the relatively low efficiencies achieved by fuel cells of the prior art. In a hydrogen-oxygen fuel cell, such inefficiencies arise principally from the non-ideal behavior of chemical reactions at the oxygen electrode. In a hydrogen-oxygen fuel cell under standard conditions, the theoretical reversible open circuit voltage in both acidic and alkaline media is 1.23 volts. Hydrogen behaves nearly ideally at the hydrogen electrode. However, oxygen does not behave ideally at the oxygen electrode. Because the oxygen electrode does not behave ideally, the experimental open circuit voltage of a typical hydrogen-oxygen fuel cell of the prior art ranges from about 0.98 volts to about 1.10 volts.
Hydrogen-oxygen fuel cells of the prior art almost exclusively operate on molecular hydrogen and molecular oxygen. The non-ideal behavior at the oxygen electrode is essentially due to the activation energy required to break down the molecular oxygen double bond for absorption onto the electrocatalyst. The double bond of an oxygen molecule has great stability. Over the entire pH range, the rest potential of the oxygen electrode is very slowly established. Values of more than 100 mV less than the theoretical oxygen potential are commonly measured. Various intermediate radicals are formed after the oxygen bond is broken, further complicating the course of reaction. The kinetics of oxygen reduction on electrocatalysts is controlled by the rate of charge transfer involving absorption of molecular oxygen, and is inhibited by these intermediaries. A low exchange current density for oxygen reduction is also observed, resulting in high activation polarization and further non-ideal behavior.
Various electrocatalysts have been investigated, but none have been able to bring the open circuit voltage close to the ideal value of 1.23 volts. This is unfortunate because if the open circuit voltage could be brought close to the ideal value of 1.23 volts, the energy conversion efficiency of present hydrogen-oxygen fuel cells would be increased by almost 20%.
Accordingly, there is a need for a fuel-oxygen fuel cell, such as a hydrogen-oxygen fuel cell, which avoids the aforementioned problems in the prior art.
The invention satisfies this need. The invention is a method of generating electricity from a fuel cell. The method employs a fuel cell having the following elements: (i) an anode, (ii) a cathode, (iii) an anode electrocatalyst disposed in electrical contact with the anode, the electrocatalyst being capable of catalyzing a fuel to positive ions, (iv) a cathode electrocatalyst disposed in electrical contact with the cathode, the cathode electrocatalyst being capable of catalyzing oxygen contained in an oxygen containing liquid to oxygen ions or hydroxyl ions, (v) a fuel inlet port for introducing the fuel to the anode, and (vi) an electrolyte electronically separating the anode from the cathode.
The method comprises the steps of (a) providing the fuel cell described in the previous paragraph, (b) providing a fuel to the anode electrocatalyst via the fuel inlet port, (c) providing an oxygen containing liquid to the cathode electrocatalyst, (d) converting the fuel to positive ions via the anode electrocatalyst and the anode, while simultaneously converting the oxygen containing liquid to yield hydroxyl or oxygen ions a the cathode electrocatalyst and the cathode, whereby an electrical potential is created between the anode and the cathode, and (e) reoxidizing the oxygen containing liquid by contacting the oxygen containing liquid with molecular oxygen. In the method, at least about 90% of the oxygen provided at the cathode is provided by the oxygen-containing liquid.